You have a time machine and can go back and just observe, without being harmed or altering either the late Cretaceous or the Pleistocene. You can only pick one. In other words, go back and see dinosaurs or go back and see ice age megafauna (saber toothed cats, mammoth, dire wolves etc).
As much as I would love to see Dinosaurs i’d pick the Pleistocene. Somehow I find it more fascinating thinking of the fantastic creatures wandering North America such a relatively short time ago than I do creatures who died 60 million years ago. It would be a bonus if I could travel to Europe and see if Neanderthals had language and what things were really like between them and early humans.
If I could see Neanderthals and Hobbits, that would be really cool. But I think seeing mammalian megafauna wouldn’t be too different from what we see today, whereas dinosaurs would be something else entirely. And if I get to see the K-T impact too…
Another vote for dinosaurs. Not that I wouldn’t really enjoy seeing woolly mammoths, saber tooth cats, et al, but there’s no way I’m missing the dinosaurs.